Automobiles, trucks, motorcycles, all-terrain vehicles, trailers, bicycles, etc. all employ pneumatic tires. Maintaining the proper pressure in the tires of these vehicles is an important factor in their safe handling, in minimizing excessive tire wear, and in achieving maximum fuel efficiency.
It is estimated that pneumatic tires can lose up to 2 pounds per square inch (psi) of pressure per month unless the pressure is properly monitored and maintained. Pressure is lost from pneumatic tires due to migration of air through the tire itself, small holes in the tire, air passing through the bead seal located at the junction of the tire and the rim, and/or leaks through the rim and the fill valve. However, vehicle operators frequently fail to monitor tire pressure often enough, and consequently do not maintain proper pressure in the tires.
There have been a number of systems proposed for automatically maintaining and/or adding air to pneumatic tires. See for example, U.S. Pat. Nos. 4,349,064; 5,556,489; 5,558,730; 6,553,010; 6,772,812; and 7,225,845. These systems have not proven to be entirely satisfactory. For example, some require a separate opening, in the rim in addition to that needed for the valve stem of the tire. This creates an added opportunity for the loss of air from the tire over time. Other systems require modification to the tire, the rim, or to the vehicle itself. Others require the use of springs to operate. Over time, the springs weaken and/or become dirty thereby reducing their ability to function properly. In addition, the use of springs in the regulation of pressure generally precludes the ability to adjust pressure without additional components and manual intervention. Many systems use sliding seals that are prone to wear. The continuous operation of these seals causes additional wear upon them even if there is no need to add pressure to the tire. Some of the systems allow the tire to become unbalanced during operation due to an unequal angular momentum caused when the pumping mechanism moves in a radial direction away from the center of the tire. Even though there have been attempts to counterbalance this factor by the addition of weight opposite the pumping device, such weights are fixed to the tire and are not synchronized with the changing momentum of the pumping mechanism. As a result, this solution only partially balances the wheel if it balances it at all.
As a result, there remains a need for a system that automatically pressurizes and regulates the pressure in pneumatic tires and that preferably does so without the need to provide either any additional modifications to the wheel, vehicle, or without the use of springs.